Posturers and posers abound in the art world. It is almost required. When someone ridicules art, why would you feel compelled to jump in and defend it? To don armor, lance and joust with the attacker? First, the art has already won. The attacker is not indifferent to it. Instead, he is affected by it. It has entered his consciousness and memory. The art and artist have done their job, even if the viewer has not entirely succumbed to the artist's intent and thinks he is above it.
Art takes care of itself.
Then there is the question of why anyone feels self appointed to be a guardian of art. It is a political move to declare oneself a gatekeeper, an assumption of power and status. A facile move for the wanna-be dominants to grab the high ground. Old-school thinking.
When a matron standing before a Van Gogh exclaims that her precious snowflake "could have done that", it is an unwitting compliment to the painter. More so if they declare that it isn't art. They're admitting that it doesn't fit their preconceptions about art, that it is new, alien and fresh to them. Or when they gasp at how expensive something is. They are defining themselves, not the work.
Art needs no defense, nor educators, critics or bloggers for a viewer to interact with it.
This does not even address what exactly is being defended...or the need for anyone to educate you.